Question

是否可以在第二个或任何下一个参数完成mySQL查询但首先是null？

例如，我为单个项目datereport生成基于给定日期（itemreport）的报告。

现在，当前端没有选择任何项目且其req.query.itemreport获得null时，考虑到用户要求所有项目而不是单个项目而不停止，则必须执行查询的其余部分执行因为它获得null参数（itemreport）。

reportsdateres.post(function(req, res, next) {

    datereport = req.query.datereport;
    itemreport = req.query.itemreport; // this can be null for querying all items

    req.getConnection(function(err, conn) {

        if (err) return next("Cannot Connect");

        var query = conn.query("SELECT SUM(total_profit) AS fee_total FROM transactions WHERE date_created = ? AND item = ?", [datereport, itemreport], function(err, rows) {
        //                                                                                                     ^^^^^^^^^^^^ 

            // do myStuff

        });
    });
});

Answer 1

reportsdateres.post(function(req, res, next) {

    datereport = req.query.datereport;
    itemreport = req.query.itemreport; // this can be null for querying all items

    req.getConnection(function(err, conn) {

        if (err) return next("Cannot Connect");

       var queryString = "SELECT SUM(total_profit) AS fee_total FROM transactions WHERE date_created = ? ";
       var queryParams = [];
       queryParams.push(datereport);

       if(itemreport){
          queryString += ' AND item = ?'
          queryParams.push(itemreport);
        }

        var query = conn.query(queryString, queryParams, function(err, rows) {
          // do yourStuff

        });
    });
});

更新

添加了修复，附加了查询字符串。即使我错过了它：）

Answer 2

reportsdateres.post(function(req, res, next) {

datereport = req.query.datereport;
itemreport = req.query.itemreport; // this can be null for querying all items

req.getConnection(function(err, conn) {

    if (err) return next("Cannot Connect");
    if (itemreport==null || itemreport=='') {
        var sql = "SELECT SUM(total_profit) AS fee_total FROM transactions WHERE date_created = ?";
        var params = [datereport];
    }else{
        var sql = "SELECT SUM(total_profit) AS fee_total FROM transactions WHERE date_created = ? AND item = ?";
        var params = [datereport, itemreport];
    }
    var query = conn.query(sql, params, function(err, rows) {
    //                                                                                                     ^^^^^^^^^^^^ 

        // do myStuff

    });
}); });

Answer 3

reportsdateres.post(function(req, res, next) {

    datereport = req.query.datereport;
    itemreport = req.query.itemreport; // this can be null for querying all items

    req.getConnection(function(err, conn) {

        if (err) return next("Cannot Connect");

        var query = conn.query("SELECT SUM(total_profit) AS fee_total FROM transactions WHERE date_created = ? AND item = COALESCE(?, item)", [datereport, itemreport], function(err, rows) {

            // do myStuff
        });
    });
});

COALESCE（我们可以在代码中删除if else）函数将第一个参数考虑在内，如果它不为null，否则它将比较item列的值与其自身，更多细节请访问：https://www.w3schools.com/sql/sql_isnull.asp < / p>

NodeJS MySQL：第二个参数为null时查询

3 个答案:

更新